Using an internal upstream URL - How does skip-upstream-tls-verify work?

I am using Keycloak Gatekeeper, and have configured an upstream URL.
The Upstream URL is internal and only accessible from within my network.

I have set ```
–skip-upstream-tls-verify true

however, I see this error:

> dial tcp: lookup <ULR> on IP:53: no such host

Is this error caused by not being able to verify the upstream URL? Shouldn't setting skip-upstream-tls-verify=true prevent this error from occurring?